In a centrifugal pump supplied fuel metering system to an engine, for example a gas turbine engine, a throttling valve must be placed down stream of the metering valve. Flow regulation for a high speed centrifugal pump for an engine is controlled with a fuel metering valve that is positioned in response to selected engine parameters. The throttle valve is arranged in series with the metering valve. The throttle valve provides a variable restriction orifice in the fuel flow path that influences the pressure drop across the fuel metering valve. The throttle valve opens and closes the variable restriction orifice to regulate a constant pressure drop across the metering valve. To keep the metering valve pressure drop constant a pressure sensor is coupled to the fuel metering valve to sense the pressure drop across the fuel metering valve. The pressure sensor controls the throttle valve position. Stability of the fuel supply pressure across the fuel metering valve is important to maintain proper engine performance throughout the range of the fuel metering operation. It is found that in systems requiring redundant fuel supply pumps maintaining stability of the fuel supply across the fuel metering valve is difficult.
Accordingly, there is a need to provide a system for metering a fuel supply that can be used in conjunction with a down stream throttling valve to provide regulation of redundant fuel supply pumps and to maintain stability of the fuel supply pressure across the fuel metering valve.
The apparatus of the present disclosure must also be of construction which is both durable and long lasting, and it should also require little or no maintenance to be provided by the user throughout its operating lifetime. In order to enhance the market appeal of the apparatus of the present disclosure, it should also be of inexpensive construction to thereby afford it the broadest possible market.
The invention provides such a fuel metering valve. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.